Metal products may be made in several ways. One way is to machine a block of cast, wrought or forged metal to a required shape. However, this frequently results in waste. A novel, but known way of constructing components is to provide metal in a fine powder form and shape it in a “can” that approximates to the desired end shape. The can is typically made of mild steel so that it is deformable, although other materials can be used. The can is filled with the powder which is then settled in the can as much as possible by vibration. Ultimately, the can is evacuated and sealed. The can is then placed in a chamber which is pressurised and heated so that the can shrinks and pressurises the powder. The grains of the powder stick together, by a process known as diffusion bonding, to form a solid block having the approximate shape of the desired end product. The composite can/block is then usually machined to remove the can, which is at this point a skin on the product, and also to remove a surface layer of the powder block to achieve desired dimensions and finish.
A known can is mild steel between 2 and 3 mm thick. Cans are normally degassed at intermediate temperatures (ca. 300° C.), sealed, preheated and then exposed to HIP in a pressure vessel. In the case of powder metallurgy (PM) superalloys, typical HIP conditions are a temperature of between 1100° C. and 1260° C., and a pressure of between 100 MPa and 200 MPa, which is maintained for several hours with argon as the pressurising medium. The superalloy powders are consolidated to full density during the HIP process by pressure assisted sintering. The can is removed by rough machining and/or pickling to reveal the near net-shape component. Compound products can also be produced by designing cans with separate compartments for different powders or enclosing parts of solid material together with the powder.
A known method of fabrication of the can is by welding together strips of mild steel to form the hollow “mould” in which the powder is contained before the HIP process is started. Fabrication in this way introduces dimensional errors through inconsistency in the process. Also, it is a time consuming process, especially if multiple components are to be made, and is not reliably repeatable. Furthermore, weld seams cannot be controlled, at least internally of the can. Accordingly, sufficient tolerance in the dimension of the finished part must be provided so that indents in the finished product, caused by unintended upstands on the internal surface of the can (at the seams) can be machined out after the HIP process has been completed and the can machined away.
As well as the production of cans for HIP manufacture by welding plates together, U.S. Pat. Nos. 4,065,303, 4,861,546 and 5,000,911 disclose production by electroplating, or otherwise coating, a blank component with a metal. The blank is then removed to leave behind the coating which forms the can.
U.S. Pat. Nos. 5,770,136, 6,355,211 and 6,042,780 also construct a mould. The mould is formed by moulding powder and binder around a blank, and ultimately filling the mould with powder. The moulded powder mould is inserted in a can (that is welded) for HIP. The can has no part in shaping the final product.
U.S. Pat. No. 5,000,911 appears to disclose:                fabricating a steel blank of the component to be formed;        creating around the blank a mould from rubber or a material that can be cut;        moulding in the mould a settable blank from wax or the like, and peeling off the rubber mould;        coating the wax blank with graphite powder and cement of the same type;        melting the wax;        filling the graphite mould with metal powder and performing HIP, the “can” so-produced being supported in powder during the HIP process.        
It is an objective of the present invention to mitigate at least some of the problems described above and provide a reproducible and effective method of metal component production using powder metallurgy technology.